This invention relates to a device for supporting transducer for use in rotary disk type storage unit and, more particularly, to a transducer supporting device in which the clearance between the transducer and the recording surface (hereinafter referred to as "floating clearance") is limited and which is suitable for a high-density storage unit improved in seek speed.
Ordinary rotary disk type storage units have a type of construction, such as the one disclosed in Japanese Patent Examined Publication No. 58-22827, which consists of a rotatable storage medium, a transducer for reading information from the storage medium or writing information thereon while being slightly spaced apart therefrom, a device for supporting the transducer, and an accessing mechanism for making the transducer reach the desired radial position on the storage medium and maintaining the transducer at the same position.
The transducer supporting device is provided with a flexible-structure member having a rectangular cutout formed with a pair of flexible outer extensions connected by a low-flexibility transverse portion, and a flexible central tongue-like portion extending from the transverse portion toward the cutout; a rigid-structure support member having a resilient portion and a load beam portion and supporting the flexible-structure support member; and a load projection disposed between the rigid-structure support member and the central tongue-like portion of the flexible-structure support member. The transducer supporting device is connected by a rigid guide arm to the accessing mechanism. An air bearing slider (hereinafter referred to simply as "slider") is attached to the central tongue-like portion of the flexible-structure support member. The load beam portion has flanges formed along its two sides facing each other in the widthwise direction perpendicular to the longitudinal direction of the supporting device, with the flanges extending in the longitudinal direction of the supporting device. The load beam portion has a shape of flattened U in transverse cross section. The combination of the rigid-structure support member and the flexible-structure support member connected to the former is called a support spring.
During seeking for accessing of the transducer at a desired radial position on the rotating storage medium, a driving force is applied from the accessing mechanism to the transducer supporting device in the radial direction of the storage medium. The transducer supporting device is accelerated, maintained at a constant speed or decelerated by this driving force.
Shaking forces are produced during seeking due to the structure of the accessing mechanism. These forces, including those applied in the seeking direction, are introduced into the transducer supporting device via the guide arm.
As stated below, the above-described type of conventional transducer supporting device was designed without giving sufficient consideration to the occurrence of changes in the slider floating clearance caused by vibrations of the transducer supporting device based on the natural vibration mode of the structure thereof when, during seeking, shaking forces due to the driving force and the accessing mechanism are applied.
That is, conventionally, this phenomenon cannot be sufficiently considered by lack of means for accurately measuring changes in the floating clearance with respect to time at a high speed and, hence, means for simultaneously measuring changes in the floating clearances at the front and rear ends of the left and right floating surfaces of the slider to detect pitching and rolling motions of the slider. What is meant by high-speed and high-accuracy measurement of changes in the floating clearances are measuring changes in the floating clearance of about 0.01 .mu.m occurring in a period of time of 0.2 ms with resolutions of 0.05 to 0.1 ms and 0.001 .mu.m or higher.
The second reason for the insufficiency of consideration of changes in the floating clearance during seeking is that the floating clearance has been considered to be sufficiently large compared with calculated changes during seeking. That is, the variation of the floating clearance in the conventional arrangement has been considered to be 0.01 to 0.03 .mu.m and has not been regarded as any serious cause of malfunctions. However, with increase in the storage density achieved recently, a need for reducing the floating clearance to 0.2 to 0.3 mm has arisen. On the other hand, it is considered that the seek speed will be increased for reduction in the access time and that the variation of the floating clearance during seeking will become larger. It is therefore necessary to sufficiently consider the problem of changes in the floating clearance during seeking.
A type of transducer supporting device in which the center axis of a load beam portion is perpendicular to the center line of slider floating rails will be described below for explanation of causes of changes in the floating clearance during seeking.
During seeking, a driving force is applied in the radial direction from the accessing mechanism to the transducer supporting device through the guide arm. Simultaneously, shaking forces including those in directions other than the driving direction are produced from moving contact portions such as traveling surfaces of the accessing mechanism and are applied to the transducer supporting device through the guide arm like the driving force. These forces excite the natural vibration modes of the accessing mechanism and the guide arm so that shaking forces other than the shaking force in the seeking direction are applied from the transducer supporting device attachment portion of the arm to the transducer supporting device in various directions including two directions perpendicular to the transducer supporting device and rotational directions. As a result, the natural vibration modes of the transducer supporting device are excited so that the slider is displaced to change the floating clearance by vibrations of the transducer supporting device. Conventionally, among the natural vibration modes of the transducer supporting device, out-plane bending and out-plane torsional vibration modes are known and means for suppressing them have been studied. However, it has been found that, apart from these modes, in-plane bending modes are excited during seeking, thereby causing large changes in the floating clearance. In these modes, the extreme end of the transducer supporting device (at which the slider is mounted) vibrates parallel to the medium surface.
Specifically, the rigid-structure support member of the conventional transducer supporting device is formed of a thin member, and the load beam portion is in the form of a channel-section member having a cross-sectional shape of flattened U and having flanges formed along its two opposite sides. The shear center of such a thin channel-section member in a transverse cross section is located remote from the bottom of the channel cross section. For this reason, the rigid-structure support member torsionally vibrates if it vibrates in the in-plane modes, thereby applying forces in the vibrating directions and torsional moments to the flexible-structure member. Consequently, these shaking forces cause pitching of the slider and, hence, large changes in the floating clearance.
As described above, conventional transducer supporting devices have been designed without giving sufficient consideration to the fact that the shear center of the rigid-structure support member in a transverse cross section is remote from the rigid-structure support member with respect to in-plane vibration modes of the same, and therefore entails the problems of the floating clearance variation being larger during seeking.
In the case of an in-line type transducer supporting device in which the center axis of the load beam portion and the center line of the slider floating rails are parallel to each other, the driving force applied form the accessing mechanism in the radial direction during seeking directly excites in-plane bending modes of the rigid-structure support member so that torsions about the shear center are large, because shaking forces are large with respect to the same shear center, resulting in increased changes in the slider floating clearance. The in-line type device therefore entails the problem of displacements of the slider in off-track directions due to rolling thereof as well as the problem of changes in the floating clearance.